1. Field of the Art
The present invention relates to heating and air conditioning systems, and more particularly, to a relatively low power auxiliary heating and air conditioning system for a motor vehicle, configured to operate when the vehicle is shut down.
2. Discussion of the Related Art
As is known, large over-the-road vehicles such as tractor-trailer trucks are used for transporting a wide variety of items. Often, the transport routes of these vehicles are extremely long, frequently extending cross-country. On such long routes the drivers of these vehicles frequently sleep within the vehicle. Accordingly, and as is known, the passenger area of a large tractor-trailer truck is typically divided into a cab area and a bunk area; the cab area being the forwardmost area, and the bunk area (also known as the sleeper) located just behind the cab area. Frequently, the bunk area is separated from the cab area by a curtain or other divider, and includes a cot on which the driver can sleep.
It can certainly be appreciated that on hot summer nights or cold winter nights, the driver will operate the air conditioning system or heating system, at least in the bunk area, to maintain a comfortable sleeping climate. Presently, this is done in any of several ways. First, the driver may leave the truck running in idle to maintain power to the heating and air conditioning system, so that the appropriate temperature in the bunk area may be maintained. Since the drivers typically sleep for several hours at a time, this approach is undesirable in that it wastes fuel and places undue wear on engine components that are left running. Furthermore, the constant engine noise is distracting, not to mention the release of carbon monoxide and other pollutants into the environment.
Another approach taken by drivers is often to superheat or supercool the bunk area, just before shutting the engine down. In this regard, the driver may direct the heating and air conditioning system to the bunk area and either overheat the area in the wintertime or cool it to an extremely low temperature in the summertime. Since the truck body provides some insulating characteristics, it takes a certain amount of time for the indoor and outdoor temperature to equalize. By superheating or supercooling the bunk area, (i.e., increasing the temperature differential), the driver can extend the time period time before the temperatures have equalized and the bunk area is uncomfortably cool or hot. Certainly, in mild climate areas, this approach is sufficient. However, in extremely harsh climates, this approach does not provide a sufficient time period of comfortable climate before the driver must restart the engine. Moreover, this approach tends to result in an uncomfortably hot or cold climate immediately after the driver shuts off the engine (i.e., the superheated or supercooled climate).
Another approach has been to utilize a self-contained heating and air conditioning system. That is, systems are known, that are independent of the vehicular heating and air conditioning system, to provide heating and air conditioning to the passenger space, and more particularly, to the bunk space of a tractor-trailer vehicle. These systems employ a small generator sufficient to power a small scale heating and air conditioning system that is directed to heat and cool the small bunk area of a tractor-trailer vehicle. Advantageously, these systems do not consume the large volume of fuel required to maintain the vehicle engine in idle. Nor do they result in the engine component wear or pollutant and noise output that result from running the engine in idle to maintain the vehicular heating and air conditioning system. These systems, however, do impose cost and space requirements that are often deemed excessive and undesirable.
Another approach known for heating and cooling the bunk space of a tractor-trailer vehicle employs the use of thermal storage media to store thermal energy during the normal operation of the vehicular heating and air conditioning system and utilize this stored energy during the down time of the vehicle to heat and cool the passenger compartment. For example, U.S. Pat. No. 5,277,038 discloses a thermal storage reservoir adapted for either cool thermal storage or warm thermal storage. A stated object of the invention described in the '038 patent is to provide additional cooling and/or heating from a thermal storage system, and to release the cooling or heating at a desired time, such as prior to entering the vehicle or during vehicle startup. Thus, the thermal storage system of the '038 patent is only directed to providing heating and cooling for temporary periods.
Indeed, it is appreciated from the architecture of the system in the '038 patent that the additional heating and cooling provided by the thermal storage reservoir is directed for providing auxiliary heating and cooling for generally short periods of time. To be sure, a prohibitive large mass of thermal storage would be required to provide extended periods of operation. This limitation is due in part to another stated object of the invention therein, which seeks to provide a system that is readily retrofit to existing vehicles with minimum modifications to the vehicle. In this regard, and as described in the '038 patent, the thermal storage means is charged for cool storage by circulation of cool air directed across a heat exchanger. This cool air is the same air utilized in the vehicle's air conditioning system, which is typically about 55.degree. F. It is known that the thermal storage capability is proportional to the product of the mass of thermal storage medium and the temperature of that medium. Thus, if the medium is charged to approximately 55.degree. F. by utilizing the existing vehicular air conditioning system, then the mass of the thermal storage system will determine the thermal storage capabilities of the system.